Plan 9 is an operating system designed by the same people who created the original UNIX. Its development began in the late 1980's and it was a research project intended to address a variety of system scalability issues that the UNIX and LINUX kernels don't do particularly well, namely, distributed computing, distributed name spaces, and distributed file systems. Plan 9 is open source and its current and fourth major release was in 2002. It is
available as an install or LiveCD and it can be downloaded here. Note: This is an entry to our Alternative OS Contest.